Lug Bolt
A threaded fastener that combines the function of a wheel stud and a lug nut, threading directly into the wheel hub assembly.
A lug bolt is a single-piece wheel fastener that combines the threaded shaft and head into a bolt, which threads directly through the wheel wheel and into matching threaded holes in the brake rotor and wheel hub assembly. This design is widely used by European car manufacturers (such as BMW, Mercedes-Benz, Audi, and Volkswagen), in contrast to the stud-and-nut system common on domestic and Asian vehicles.
Lug bolts feature either a tapered (cone) or ball (radius) seat beneath the bolt head, which matches the mounting holes on the wheel. The correct seat type is critical: using a cone-seat bolt on a ball-seat wheel will prevent proper torque distribution, causing the bolt to loosen and damage the wheel. Lug bolts must be hand-threaded first to prevent cross-threading the hub holes, which are expensive to repair.
When removing a wheel secured by lug bolts, the wheel can fall off the hub flange as soon as the last bolt is removed because there are no studs to support its weight. Technicians often use a temporary wheel hanger tool (a threaded guide pin) screwed into one of the hub holes to support the wheel during removal and installation. Lug bolts should be inspected for thread stretching and torqued in a star pattern.